In a radio system linearity of a power amplifier limits the obtainable maximum transmit power, especially when the signal to be transmitted has a high peak to average power ratio (PAPR). In such a case the signal input to the power amplifier may exhibit momentarily high power that must be taken into account in designing the power amplifier. This means in practice that an output signal of the amplifier is scaled down to a lower power level in order to meet the spectral requirements of the data transmission system currently in use. Due to this, the signal to be amplified is biased such that the transfer function of the amplifier becomes more linear. However, this reduces the efficiency of the amplifier and/or the transmitter. Secondly, power amplifiers with a broad linear operating range are expensive.
Signal components exceeding a threshold can also be clipped by limiting the peak values to the threshold. The other signal values below the threshold are not changed. However, a problem with the clipping methods is that the signal frequency spectrum spreads, i.e. usually the spectrum spreads beyond the frequency band that is used, thus causing interference to other users. If the spreading of spectrum is limited, the PAPR remains high.